There are conventionally two types of multi-lamp shadowless illumination systems used in medical environments. One is a single lamp housing type in which a number of lamps are mounted in a single lamp housing. The other is a multi-lamp housing type in which a number of lamps are sealed within separate lamp housings which in turn are linked together by a connecting pipe.
In the single lamp housing type, the depth of focus of the system, i.e. distance from the lamps of the point at which the axes of the lamps converge, is adjusted by tilting each lamp within the lamp housing. As far as the inventor is aware, however, the depth of focus in a multi-lamp housing type is fixed, and there is no system of this type available which is equipped with a lamp-tilting device to change the focal depth.
Recently the use of so-called "clean air" type operating rooms, which are freed from bacteria and dust by discharging dirty air and introducing clean air, has been increasing. In such rooms single lamp housing type illuninating systems using a bulky lamp housing are not desirable. The reasons are that the top surface of the lamp housing is so large that dust and other deposits collect naturally on such a large area; and when clean air is introduced, the collected dust falls on the body of a patient being treated and is likely to cause a secondary infection in the patient due to bacteria or the like.
Thus for a "clean air" operating room, adoption of a multi-lamp housing type of shadowless illumination system is preferable.
However, with a multi-lamp housing type of shadowless illumination system there is the inconvenience of moving all the lamp housings to focus the light depending on the position of the patient's body, because the systems are a fixed focus type system, as stated above. Moving all the lamp housings is not only strenuous work but is also likely to cause stirring up of dust, even if in small quantities, which is undesirable from the standpoint of medical treatment or sanitation.
Thus the medical world has desired a multi-lamp housing type shadowless illumination system which is equipped with means within the lamp housing for adjusting the depth of focus by merely changing the angle of each lamp instead of moving all the lamp housings.